Prior art of possible relevance includes U.S. Pat. Nos. 1,927,325 issued Sept. 19, 1933 to Ritter; 3,437,134 issued Apr. 8, 1969 to Oddy; and 4,449,581 issued May 22, 1984 to Blystone et al; and Australian Patent Specification No. 236,342 accepted Nov. 7, 1961. So-called plate fin heat exchangers have been used with considerable success in various heat exchange operations requiring the exchange of heat between a liquid and a gas or a gas and a gas. In the usual case, a plurality of relatively thin plates are disposed in slightly spaced, parallel relationship to form a stack of such plates which serve as fins. A plurality of tubes, in one or more rows, pass through aligned holes in each of the plate fins at generally right angles to the plane defined by each and by means of manifolds or the like are placed in fluid communication with each other to permit the circulation of a fluid, usually a liquid, through the resulting heat exchanger core.
In order to assure maximum heat transfer in such a core, it is necessary that the fins make good heat exchange contact with the tubes; and this is typically accomplished by making the relevant exterior dimensions of the tubes a few thousandths of an inch larger than the tube holes or openings in the plates. Thus, when the tubes are inserted in the holes, a snug fit with good contact results to maximize heat transfer through the junction.
This same snug fit can present difficulties in the assembly operation. For one, it means that the tubes must be forced through the holes, a process commonly referred to as "tube pushing". If the forces required to perform the tube pushing operation exceed the strength of the fins, the fins will bend which, at the very least, will result in a core having a poor appearance which may be perceived as shoddy workmanship. At worst, the bending may become so severe that the core cannot be successfully assembled in its entirety and will have to be scrapped.
To avoid these difficulties, it is heretofore been common to form the fins of plate stock that is thicker than is required for optimum heat transfer performance simply to attain the degree of structural integrity necessary to resist bending during the tube pushing operation. This, of course, not only adds to the material expense of the core, but will increase the weight of the same. In some applications, as, for example, vehicular applications, the excess weight is undesirable in that it will increase the energy costs for operating the vehicle.
The problem becomes particularly acute where the tubes are in multiple rows and as a consequence, the pushing of the fins in the central rows tend to cause the plate fins to bend or bow.
The problem is also acute in constructions where the tube in the multiple rows are aligned, so-called flat or oval tubes the presence of the tube holes of the aligned tubes in the direction of elongation of the flattened tubes frequently will result in the removal of in excess of 50% of the fin material at the location of alignment. Consequently, the fins are very prone to bending at such location.
The present invention is directed to overcoming one or more of the above problems.